Excerpt from the report Summary: The first comprehensive life-cycle inventory (LCI) for biodiesel produced in the United States from soybean oil was completed by Sheehan et al. in 1998. The purpose of the study was to conduct a life-cycle assessment (LCA) to quantify and compare the environmental and energy flows associated both with biodiesel and petroleum-based diesel. One of the most often cited results from Sheehan et al. is that the fossil energy ratio of biodiesel is equal to 3.2. In other words, biodiesel yields 3.2 units of energy for every unit of fossil energy consumed over its lifecycle. By contrast, it was found that petroleum diesel’s life cycle yielded only about 0.84 units of energy per unit of fossil energy consumed. The purpose of the following analysis is to update the energy life cycle of the model to determine if any significant changes in the original inventory have occurred since the model was first developed 10 years ago.